Early adversity and individual differences in the endogenous oxytocin system (#249)

The endogenous oxytocin mediates a large range of effects, from lactation and birth to facilitation of social interaction. Research shows that individual differences in oxytocin levels in animals and humans are quite large. Human research shows large differences in basal levels of oxytocin, but also in response to challenges, which have been correlated with various behavioural differences. Only limited research has been conducted on the origin of these individual differences. Large differences seem to exist between species in the distributions of oxytocin (and vasopressin) receptors that appear to correlate with the sociality of these animals. A review of the literature shows that differences in the oxytocin system can be based on individual factors, e.g. genetic variation especially in the oxytocin receptor, age or gender, or be the result of early environmental influences such as social experiences, stress or trauma. This paper explores the factors that cause individual differences in the oxytocin system and the environmental factors that have been identified to induce long-term changes in the developing oxytocin system during different life phases.The following differences in the oxytocin system could have functional outcomes that translate into behavioural differences: expression of oxytocin and its receptor; number, location and sensitivity of receptors; and connectivity with other systems. It is suggested that early life adversity can change the development of the oxytocin system and the way it modulates other systems. Individuals may show only minor differences in behaviour and function unless subsequent stressors challenge the system. It is postulated that at that time individual differences in oxytocin levels, reactivity of the system or interactions with other systems can influence general resilience and the susceptibility to develop mental health and addiction.